1. Field of the Invention
The present invention relates to a four-wheel drive vehicle such as a utility vehicle.
2. Related Art
As disclosed by US 2010/0120565 A and JP 2012-171609 A, a conventional four-wheel drive vehicle that is adaptable as a utility vehicle is equipped with a power unit and front and rear transaxles. The power unit includes a prime mover (e.g., an engine), a speed-changing gear transmission and a belt (or sprocket) type transmission interposed between the prime mover and the speed-changing gear transmission.
The front and rear transaxles carry drive wheels provided with respective brakes. The vehicle is provided with a manipulator such as a brake pedal for braking all the drive wheels with all the brakes. However, the brakes have small capacities because the drive wheels have small spaces for mounting the respective brakes. If the vehicle has to be stopped on a slope, the insufficient braking force applied on all the drive wheels by all the brakes may cause the vehicle to unexpectedly descend the slope.
In this regard, as disclosed by Japanese Patent No. 3684221 (hereinafter, referred to as '221), a conventional four-wheel drive vehicle is equipped with the power unit and front and rear transaxles, and with a parking brake on the rear transaxle. This parking brake assists the braking of drive wheels with brakes provided on the respective drive wheels. The reference '221 also suggests that a power take-off shaft provided with the parking brake may be divided into front and rear divisional shafts and a clutch for selecting a drive mode of the vehicle between a 2WD (two-wheel drive) mode and a 4WD (four-wheel drive) mode may be interposed between the divisional shafts. However, the reference '221 does not suggest any association of the clutch with the parking brake.
If the vehicle set in the 2WD mode has to be stopped on a slope, an operator will manipulate the braking manipulator (such as the brake pedal) for braking all the drive wheels with the respective brakes, and may further manipulate a parking brake manipulator for activating the parking brake, however, the braking force caused by the parking brake is applied to only the two drive wheels receiving the output power from the power unit. The remaining two drive wheels that are isolated from the output power of the power unit by disengaging the drive mode selection clutch are braked by only the respective brakes without the parking brake. This braking of the remaining drive wheels without the parking brake may be insufficient to surely stop the vehicle on a vehicle, thereby causing the vehicle to unexpectedly descend.
To surely stop the vehicle on the slope, an operator may have to manipulate for shifting the drive mode selection clutch to the 4WD mode state in addition to the braking manipulation for all the brakes on the drive wheels and the parking brake manipulation for the parking brake so as to apply the parking brake force caused by the parking brake to all the drive wheels. However, an operator is liable to forget such an additional manipulation for the drive mode selection clutch, thereby causing the insufficient parking brake because the vehicle is left in the 2WD mode.